In internal combustion engines, when the combustion temperatures exceed about 2,500° F. (about 1,371° C.), atmospheric nitrogen begins to react with intake oxygen to form compounds called nitrogen oxides (NOx). These compounds play a major role in air pollution, particularly in high traffic areas such as cities. To reduce the formation of NOx, combustion temperatures must be kept below the 2,500° F. threshold. One way this is achieved is by re-circulating a small amount of engine exhaust back into the engine intake through an exhaust gas recirculation (EGR) valve.
The EGR valve controls a passageway between the intake and exhaust manifolds. Sensors and a control unit are used to open the valve to allow the intake vacuum to draw exhaust through the valve and into the intake stream. The exhaust gas dilutes the incoming air/fuel mixture and has a quenching effect on combustion temperatures, which keeps NOx production within acceptable limits. As an added benefit, it also reduces the engine's octane requirements which lessens the occurrence of detonation (spark knock).
However, when a waste heat recovery system is also used to recover energy from the exhaust flow before it enters the intake side, condensation formation at the engine intake can pose other problems. Condensation on the intake system may damage the engine by breaking down oil film on engine cylinder surfaces and clogging intake ports by combining with combustion soot to form wet soot deposits. The main cause of the condensation is an EGR out temperature which is too low as a result of the temperature of the working fluid in the WHR being much lower than the engine coolant temperature.
The disclosed system and methods address these problems in the prior art by providing protection against condensation production. The system provides means for protecting against cooling the EGR stream beyond a threshold which would cause condensation. Likewise, the methods provide for protecting an engine from damage due to heavy condensation at the intake system.